Next-Generation Serial Storage Moves Ahead

The next generation of serial storage technologies is moving ahead, with vendors starting to roll out the first Serial ATA II (SATA II) and Serial Attached SCSI (SAS) products.

ARIO Data Networks has followed up on its February release of SATA controllers with its first SATA II and SAS controllers. SATA II doubles SATA's speed to 3Gbps, and SAS is the serial successor to parallel SCSI.

“SATA II and SAS are both killer technologies ... Now I can create a pool of SAS drives for faster response and performance and reliability, and a pool of SATA drives for inexpensive bulk storage in the same box.”

 Arun Taneja, The Taneja Group

ARIO says its controller board products will be available in the fourth quarter. The SATA II and SAS controllers are based on the company's high-performance ASIC technology, the basis of the 10,000 SATA I products ARIO has shipped to date. The controllers will offer several different options for host connectivity, including 4Gbps Fibre Channel, SAS, and iSCSI host interconnects.

LSI director of industry marketing Harry Mason, who also serves as president of the SCSI Trade Association, says he expects all the pieces for SAS subsystems to be production-ready by the end of the third quarter, with some production shipments occurring by the end of the year.

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Analysts say serial storage technologies have a bright future — and it's even brighter because SAS developers had the foresight to make SAS
backplanes compatible with SATA.

"SAS makes a ton of sense since it is plug compatible with SATA," says Tony Asaro of the Enterprise Storage Group's ESG Lab. "If you can support a shelf
of SATA, then you can support a shelf of SAS. I believe SAS will actually challenge Fibre Channel for the enterprise drive of choice. SAS is just SCSI, but with serial connectivity."

"The biggest challenge with SCSI for external storage is the ergonomics, which SAS solves," says Asaro. "But SAS is just as reliable, and the performance is just as good as FC at 10,000 and 15,000 RPMs, but it is cheaper."

"I believe that the combination of SAS and SATA is a winner," Asaro continues. "With SATA, you get low-cost, lower performance, high-density drives with arguably greater failure rates. With SAS, you get a higher price than SATA, but lower than FC with the same level of reliability, performance, and density as FC. I think you will see SAS being implemented in stages by the end of 2004 and throughout 2005."

SATA drives cost about 75% less than Fibre Channel drives, according to Taneja. "Yes, they are less reliable than FC drives," he says. "Yes, they are slower (in rotational speed). But for a lot of applications they are ideal, especially given their pricing advantage ... I think SATA and SATA II will take the enterprise by storm."

SAS "was going to be a big loser as SATA came in," Taneja continues. "But SAS did one thing very right: They made the physical interface the same as SATA. That means I can plug a SAS or a SATA drive in the same connector. That means now I can create a pool of SAS drives for faster response and performance and reliability, and a pool of SATA drives for inexpensive bulk storage in the same box. Do you see the makings of ILM? Yes, that is where the play will be."

"I thought SAS had lost it until they made that decision," he says. "Now they will co-exist with FC and SATA moving forward."

Enterprise Storage Group analyst Peter Gerr reports that every major vendor but HDS is shipping systems with SATA drives, and he expects HDS "to follow suit shortly." Many emerging vendors, such as Copan, 3Par, Isilon, ONStor, and Pillar, "use SATA exclusively or as a complement to the FC drives they also support," says Gerr.

Among startups that are using SATA for primary storage, "so far we know of no major disasters," reports Asaro.

Some vendors are taking steps to improve the reliability of native SATA drives, such as dual-porting them like FC drives, Gerr says. Copan has developed a proprietary implementation called Disk Aerobics that does controlled power-up and power-down of individual drives as needed to handle I/O requests, according to Gerr.

"Personally, I've yet to hear of or speak to an enterprise user that isn't satisfied with their SATA solution, and while these systems are typically being used as backup-to-disk targets, or lower-cost repositories for bulk data — perhaps to stage to disk before being backed up to tape — some users are implementing SATA in near-production environments," Gerr says.

"While current generation SATA drives don't offer the 10,000-15,000 RPM speeds that FC does and high-volume I/O-intensive applications demand, to me, and to users that are struggling to store more of their valuable data online more of the time, the cost benefits are much more compelling than any supposed reliability issues, if used in the appropriate use cases," Gerr continues.

Gerr also says he's concerned that drive manufacturers, facing margin pressures from low-cost SATA drives, "may position SAS's performance and reliability benefits as justification to command a higher price than SATA. To me, this would be detrimental to both the adoption of SATA, and the emergence of tiered storage architectures, which to me, are fundamental prerequisites to enabling utility-class storage environments."